There is a need for part production of straighter parts in the field of plastic injection molding. Existing plastic injection practices reliably produce plastic parts of certain measured straightness, but falls short when very straight parts are needed, especially when molding longer parts such as pipettes. Pipettes are typically used to measure and deposit precise amounts of a liquid into a target container. Often an array of pipettes is arranged in parallel for parallel depositing into multiple targets such as cylindrical containers. Using warped or bent pipettes increases the potential of one target receiving the liquid from two pipettes while an adjacent target receiving none of the liquid. Therefore, the users of pipettes have been requesting straighter and straighter parts that were previously difficult to produce.
In plastic injection molding, molten plastic is injected into a mold and the molten plastic flows until filling up the entire mold, then the plastic solidifies and the finished part is ejected from the mold. For long parts, such as pipettes, in prior methods, the plastic enters one location of the mold and cools at different rates on each side of the part, thereby causing a slight bending of the parts that leads to straightness issues with respect to the linearity (or straightness) of the resulting parts. Typically, the parts bow inwards towards the hot side of the tool resulting in uneven shrinkage between opposing sides. To reduce this difference, dual gate systems have been introduced to allow entry of the molten plastic from, for example, two sides of the mold, but issues exist with this technology due to the delivery of the molten plastic not being balanced and symmetrical. For example, if the injection channels are of differing length, thickness, and/or initial temperatures.
Another issue in injection molding is waste, typically created in the injection process by runners—the plastic in excess of what is needed to produce the plastic part, typically ejected from the mold along with the part. Such runners are typically ground and sold for use in other applications that require lower tolerances and applications that are capable of utilizing non-virgin material; typically at a greatly reduced price over the virgin plastic. Therefore, it is financially important to reduce or eliminate waste caused by runners.
What is needed is a system that will mold precision plastic parts.